Kazushige Hori

Tris-bridged [3.3.n](3,6,9)carbazolophanes 1n (n = 3-6), which are appropriate model Compounds for fully overlapped excimer in carbazole chromophore, have been synthesized and characterized by NMR, X-ray, absorption and fluorescence spectra; lit showed excimeric fluorescence, whose emission maxima strongly depended on the angles and distances between carbazole rings.

Inter-moiety electronic interactions in the singlet and triplet excimer states of triply bridged [3.3.n](3,6,9)-carbazolophanes ([3.3.n]Cz, n = 3-6) were studied by emission and transient absorption measurements. In these [3.3.n]Cz molecules, the dihedral angle and the separation distance r between fully overlapped two arbazole rings change systematically from nearly parallel (n = 3, r = 3.35 A) to oblique (n = 6, r = 4.03 angstrom). In rigid glass at 77 K, [3.3.n]Cz (n = 3, 4) (r < 4 angstrom) exhibited red-shifted and structureless excimer fluorescence and phosphorescence while [3.3.n]Cz (n = 5, 6) (r > 4 angstrom) exhibited monomer-like vibrational fluorescence and phosphorescence. In solution at 130 K, all [3.3.n]Cz molecules exhibited an excimeric fluorescence band while [3.3.5]Cz still exhibited monomer-like phosphorescence. Transient absorption spectra measured at 294 K exhibited local excitation and charge-transfer bands for all [3.3.n]Cz molecules in the excited singlet and triplet states, suggesting that not only singlet but also triplet excimers of carbazole are formed at room temperature. Furthermore, the singlet-triplet energy gap decreased with the decrease in n, suggesting that electrons are effectively delocalized over the two carbazole moieties. These findings showed that both singlet and triplet excimers of carbazole are formed with a separation distance shorter than about 4 angstrom and are most stable in the parallel-sandwich structure and that the configurational mixing between exciton resonance and charge resonance states plays an essential role in the formation of singlet and triplet excimers of carbazole.

Cyanamide- andoxa-bridged [3.n](3,9)carbazolophanes 1n and 2n (n = 4 and 5) were synthesized. X-ray analysis Of 14 and 25 revealed that carbazole rings are taken to be partially overlapped geometry. Electronic spectra of 1n and 2n (n = 4 and 5) showed the existence of transannular pi-pi electronic interaction between two carbazole rings, whereas fluorescence of these carbazolophanes indicated monomer-like emission.

Asymmetric epoxidation of (E)-chalcone with alkaline hydrogen peroxide by novel chiral phase-transfer catalysts (chiral PTCs) with quaternary ammonium salts of azacrown ether proceeded in high yield and good enantioselectivity. Remarkably, this reaction depended on the length of the carbon chain on the nitrogen atom with the chiral PTCs and on the bulk of the base. (c) 2006 Elsevier Ltd. All rights reserved.

The photophysical properties of a series of triply bridged [3.3.n](3,6,9)carbazolophanes ([3.3.n]Cz, n = 3, 4, 5, 6) were studied as a model compound for a fully overlapped carbazole excimer. In these [3.3.n]Cz molecules, a plane angle of the two carbazole moieties changed systematically from nearly parallel to oblique, with increases in the length of the methylene chain n bridging at the 9-position of each carbazole ring. Absorption bands of [3.3.n]Cz showed the blue-shift and the splitting for L-1(a) <- (1)A and L-1(b) <- (1)A transition bands of the reference carbazole monomer, respectively. These spectral changes in [3.3.n]Cz were explained by Kasha's molecular exciton theory with the distance r and dihedral angle theta between the carbazole moieties in the ground state. In both liquid and glass matrixes, [3.3.n]Cz showed intramolecular excimer emission. The emission peak wavelength changed from 409 nm (n = 6) to 480 nm (n = 3) depending on r in the ground state. The dependence of the peak wavelength on r clearly showed that relative configurations of carbazole moieties in the ground state were preserved even in the excimer states. The smaller radiative rate of the excimer emission than the reference monomer was explained by the dimer symmetry of [3.3.n]Cz.

As a first example of carbazole-acceptor cyclophane, carbazole-terephthalate cyclophane 1a was prepared. The structure of 1a was characterized by H-1 NMR and X-ray analysis. Absorption spectrum of 1a showed the existence of transannular pi-pi electronic interaction and little charge transfer interaction. Fluorescence spectrum of 1a in THF exhibited intramolecular exciplex emission around 525 nm.

The acyl group of an alpha-aryl-beta-keto ester was readily transferred to N-, O-, and S-nucleophiles. The transacylation from arylated diethyl 3-oxoglutarate to amines led to unsymmetrical malonic acid amide esters in high yields. The present reaction proceeded under mild conditions without formation of detectable byproducts. Only simple experimental manipulations were required. This reaction was also found to be sensitive to steric factors, which enabled the chemoselective monoacylation of diamines and amino alcohols without any modifications such as protection.

3-Methyl-5-nitropyrimidin-4(3H)-one readily reacts with carbonyl compounds to produce three kinds of ring transformations. The nitropyrimidinone behaves as the synthetic equivalent of activated diformylamine affording 3,5-difunctionalized 4-pyridones, 4,5-disubstituted pyrimidines and functionalized 4-aminopyridines. It also behaves like alpha-nitroformylacetic acid to give 5,6-disubstituted 3-nitro-2-pyridones.

Asymmetric decomposition of isoxazolidine derivatives under catalysis by optically active palladium(ii) complexes was examined. When racemic ethyl cis-2,5-dimethyl-5-phenylisoxazolidine-3-carboxylate (cis-1a) was treated with a catalytic amount of [Pd(MeCN)(2){(S)-TolBINAP}](BF4)2 in CH2Cl2 for 60 h, optically active substrate was recovered with 99% ee and in 48% yield. The highest selectivity was achieved on treatment of racemic ethyl trans-2,4-dimethyl-5,5-diphenylisoxazolidine-3-carboxylate, to give the optically active substrate in 74% yield with 35% ee. The k(f)/k(s) value of this reaction reaches as high as 732. For this decomposition, each substrate should have both a methyl group on the 2-position and an alkoxycarbonyl group on the 3-position of the isoxazolidine ring. The enantioselectivities of the recovered substrates were influenced not only by the other substituent groups on the 4- and 5-positions but also by the geometrical structures of the substrates.

[2.2]Paracyclo(3,6)carbazolophane (1a) and [2.2](1,4)-naphthaleno(3,6)carbazolophane (1b) were prepared. The structures of 1a and 1b were characterized by H-1 NMR. X-ray analysis of 1a revealed that the carbazole ring extremely deviates from the conjugated plane. Electronic spectra of 1a and 1b showed the broadening and bathochromic shift compared with the references.

2,3-Disubstituted 2,3-dihydro-6-nitro-1H-[1,4]-diazepines are prepared with easy experimental manipulations from formylated nitroenamine, which behaves as the synthetic equivalent of nitromalonaldehyde usable in organic media.

Polyfunctionalized pyrrole 6 is synthesized in the ring transformation of N-hydroxy-3,5-dinitro-4-pyridone 4 with enolate 2 derived from diethyl 3-oxogulutarate. The present reaction proceeds with C-N transfer from 4 to 2, which is hitherto unknown manner in similar reactions using dinitropyridone series.

The title compounds are readily available by ring transformation of nitropyrimidinone with active methylene compounds in the presence of ammonium acetate.

New methods for functionalization of 1-methyl-2-quinolone (MeQone) skeleton are provided. The reaction of 1-methyl-3,6,8-trinitro-2-quinolone (TNQ) with amines affords quinolone dimer 1 and 6,8-dinitroquinotone (6,8-DNQ). Dimerization predominantly proceeds at room temperature, and denitration takes place under heated and diluted conditions. We also provide a plausible mechanism for these reactions on the basis of structure-reactivity relationship of amines. (C) 2002 Elsevier Science Ltd. All rights reserved.

A novel synthetic procedure for 3-nitro-2-pyridone derivatives (2) is provided, which includes the ring transformation of 1,3-dinitroquinolizin-4-one (3) with ketones in the presence of ammonium acetate.

New BINOL-derived ligands, 3,3'-bis(2-oxazolyl)-1,1'-bi-2-naphthols (BINOL-Box), bearing chiral bis-oxazoline at the 3,3'-carbons, were synthesized from commercially available 1,1'-bi-2-naphthol (BINOL). With the new ligands obtained, we found that asymmetric 1,3-dipolar cycloaddition reaction of N-benzylidenebenzylamine N-oxide (2) to 3-((E)-2-butenoyl)-1,3-oxazolidin-2-one (1) was catalyzed by BINOL-Box-scandium complexes to give isoxazolidine 3 in high yield with high diastereo- and enantioselectivity. For example, the reaction of 1 with 2 catalyzed by a 6 mol% (S,R)-7d and 5 mol% Sc(OTf)(3) complex proceeded to give the endo-3 as the major diastereomer with an endo:exo ratio of 97:3 and 87% ee of the endo-product in the presence of 4 Angstrom molecular sieves. Interestingly, the absolute configuration of the major product was changed according to the kind of additive used. (C) 2000 Elsevier Science S.A. All rights reserved.

Chiral phosphinepalladium(II)-catalyzed asymmetric 1,3-dipolar cycloaddition of nitrones to alpha,beta-unsaturated carboxylic acid derivatives has been investigated. In the presence of a catalytic amount of [Pd(NCMe)(2){(S)-tolbinap}](BF4)(2) [TolBINAP = 2,2'-bis(di-p-tolylphosphino)-1,1'-binaphthyl], the reaction of 3-alkenoyl-1,3-oxazolidin-2-ones as dipolarophiles and N-substituted N-benzylidenenitrones has been successfully performed to give isoxazolidine derivatives in high yields with high enantioselectivities. For example, 3-((2,5-dimethyl-3-phenylisoxazolidin-4yl)carbonyl)-1,3-oxazolidin-2-one was obtained from the reaction of N-benzylidenemethylamine N-oxide and 3-crotonoyl-1,3-oxazolidin-2-one in 89% yield with 60% endo selectivity and 91% ee of the endo isomer. The cycloaddition of N-benzylidenebenzylamine N-oxide and 3-crotonoyl-1,3-oxazolidin-2-one afforded 3-((2-benzyl-5-methyl-3-phenylisoxazolidin-4-yl)carbonyl)-1,3-oxazolidin-2-one in 94% yield with 93% endo selectivity and 89% ee of the endo isomer. Remarkably, the endo/exo selectivity of the products depended on the N-substituent group of the nitrones. These selectivities were explained using molecular modeling.

The intramolecular nucleophilic addition of 2-allylphenol was catalyzed by RuCl3. nH(2)O/AgOTf-PPh3-Cu(OTf)(2) to afford 2,3-dihydro-2-methylbenzofuran in good yield, while 2-(3-butenyl)phenol was converted to 3,4-dihydro-2(2H) -methylbenzopyran.

The 1,3-dipolar cycloadditions of enol ethers as electron-rich olefins with C-phenyl-N-alkyl nitrones proceeded smoothly in the presence of easy handling palladium(II) catalysts under mild conditions to give isoxazolidines in good yield. (C) 1998 Elsevier Science Ltd. All rights reserved.

Asymmetric 1,3-dipolar cycloaddition of nitrone 2 to olefin 1 was catalyzed by chiral phosphine-palladium complexes to give isoxazolidine 3 in high yield with high enantioselectivity up to 91% ee. Copyright (C) 1996 Elsevier Science Ltd